Field of the Invention
The present invention is directed to a low impedance VDMOS semiconductor component having a planar gate structure. The component is formed of a semiconductor body of a first conductivity type having two main surfaces that are essentially opposite to one another. A highly doped first zone of the first conductivity type is provided in an area of one of the main surfaces, whereby the first zone is separated by a second zone of a second conductivity type from the semiconductor body. The first zone and the second zone are interspersed with a trench reaching up to the semiconductor body. Such a VDMOS semiconductor component of low impedance can be a VDMOS field effect transistor, in particular, and can be a bipolar transistor with an insulated gate (IGBT). Furthermore, the present invention relates to a method for producing such a VDMOS semiconductor component of low impedance.
FIG. 4 shows a traditional low impedance trench MOS field effect transistor for voltages between approximately 20 to 100 V (also compare U.S. Pat. No. 4,941,026). The traditional trench MOSFET has a semiconductor body 1 with an n+-doped drain zone 2, an n-doped semiconductor zone 3, a p-doped semiconductor zone 4 and with an n+-doped source zone 5. An annular trench 6, whose wall is covered with an insulating layer composed of silicon dioxide, for example, and which is filled with an n+-conducting polycrystalline silicon 8, extends through the source zone 5, the semiconductor zone 4 and the semiconductor zone 3 up to the drain zone 2.
A metallization 9 composed of aluminum, for example, is situated on the semiconductor body 1, which is composed of correspondingly doped silicon, for a grounded source electrode S. The drain zone 2 is connected to a drain electrode D at which a drain voltage +UD is adjacent. The polycrystalline silicon 8 is connected to a gate electrode G.
Such a traditional trench MOS field effect transistor is of low impedance and can be used for voltages between approximately 20 to 100 V without further ado. However, it is relatively complicated to produce due to the deep trench gates.
FIG. 5 shows another traditional MOS field effect transistor, which is referred to as a xe2x80x9cHEXFETxe2x80x9d, for example. It is composed of the semiconductor body 1 with an nxe2x88x92-conducting drain zone 10, an nxe2x88x92-conducting semiconductor zone 11, an n-conducting semiconductor zone 12, an p-conducting annular semiconductor zone 13, and with n+-conducting semiconductor zones 14. The semiconductor body 1, with its respective zones 10 to 14, is formed of correspondingly doped silicon (see example of FIG. 4).
A drain contact 15, at which the drain voltage +UD is present, is attached to the semiconductor zone 10. On the side of the semiconductor body 1 that is opposite the drain contact 15, a gate electrode 17 composed of n+-doped polycrystalline silicon is embedded into a gate oxide layer 16 composed of silicon dioxide, for example. A metallization 18 composed of aluminum, for example, is also situated on the surface side for contacting the source zones 14.
A MOSFET having the structure as shown in FIG. 5 is simpler to produce than the MOSFET of FIG. 4. However, it is more surface-involved, since a trench is not provided there.
It is accordingly an object of the invention to provide a low impedance VDMOS semiconductor component which overcome the above-mentioned disadvantages of the prior art devices and methods of this general type, which can be produced in a simple way and requires a minimal surface area.
With the foregoing and other objects in view there is provided, in accordance with the invention, a low impedance VDMOS semiconductor component having a planar gate structure. The VDMOS semiconductor component contains a semiconductor body of a first conductivity type having two main surfaces, including a first main surface and a second main surface disposed substantially opposite to one another. A highly doped first zone of the first conductivity type is disposed in an area of the first main surface. A second zone of a second conductivity type separates the first zone from the semiconductor body. The first zone and the second zone have a trench with a bottom formed therein reaching down to the semiconductor body. An insulating material fills the trench at least beyond an edge of the second zone facing the semiconductor body. A region of the second conductivity type surrounds an area of the bottom of the trench.
It is advantageous that the region of the second conductivity type reaches up to the second zone and that the trench filled with the conducting material is filled with the conducting material at least up to the edge of the second zone facing the one main surface.
It is also expedient that at least one further region of the second conductivity type is provided in the semiconductor body below the region of the second conductivity type.
It is possible to completely fill the trench with the insulating material when the semiconductor component is an IGBT.
Glass such as xe2x80x9cflow glassxe2x80x9d can be used for the insulating material. Furthermore, it is advantageous that an upper epitaxy layer is doped higher in the semiconductor body than epitaxy layers lying there below.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for producing a low impedance VDMOS semiconductor component. The method includes the steps of: providing a semiconductor body of a first conductivity type having two main surfaces, including a first main surface and a second main surface disposed substantially opposite to one another; providing a highly doped first zone having the first conductivity type disposed in an area of the first main surface in a second zone of a second conductivity type separating the first zone from the semiconductor body; forming a trench having a bottom extending through the first zone, the second zone and reaching down to the semiconductor body; filling the trench with an insulating material at least beyond an edge of the second zone facing the semiconductor body; and forming a region of the second conductivity type to surround an area of the bottom of the trench. The region is produced by out-diffusion of a dopant of the second conductivity type from the area of the bottom of the trench.
A method for producing a semiconductor component of the aforementioned species is characterized in that the region of the second conductivity type is formed by out-diffusion of a dopant of the second conductivity type from the area of the bottom of the trench. If the first conductivity type is n-conducting, boron is preferably provided as a dopant for the second conductivity type. In this case, the boron is out-diffused from the area of the bottom of the trench.
The dopant, namely boron in the present example, can be previously introduced by ion implantation into the area of the bottom of the trench.
The inventive method, therefore, represents a slight modification of a VDMOS process with a self-adjusting contact hole for the trench; after the trench has been deeply etched, the dopant of the second conductivity type, such as boron, is implanted and out-diffused from the bottom of the trench. Subsequently, the trench is partially filled up with the insulating material, particularly xe2x80x9cflow glassxe2x80x9d, whereby the pn-transition between the first zone and the second zone remains free in the trench. The region created by the out-diffusion of the dopant of the second conductivity type reaches the second zone of the second conductivity type, so that, overall, a continuous p-conducting region arises in the area around the bottom of the trench up to the first zone of the first conductivity type when boron is used for the out-diffusion. Further xe2x80x9cburiedxe2x80x9d regions of the second conductivity type, which are situated below the region of the second conductivity type, can be potentially provided. Such further regions of the second conductivity type can be created by epitaxial eliminations of individual semiconductor layers and implantations.
Finally, a metallization is performed after the individual steps for creating the region of the other mode of conductivity have been carried out.
Advantageously, an upper epitaxy layer is doped higher in the semiconductor body than layers lying there below. Therefore, an upper epitaxy layer, in which the first zone of the first conductivity type and the second zone of the second conductivity type are situated, is nxe2x88x92-conducting when the region of the second conductivity type is p-conducting as a result of the out-diffusion of boron. The epitaxy layers provided there below then are n-conducting.
Overall, a low impedance VDMOS semiconductor component thus arises wherein the conductivity of the current path is approximately double in the n-conducting semiconductor body, so that the turn-on resistance can be reduced by half. A further region of the second conductivity type below the region of the second conductivity type is already sufficient for applications below approximately 100 V. Correspondingly more regions of the second conductivity type can be provided for higher voltages.
The inventive VDMOS semiconductor component preferably is a VDMOS field effect transistor. The invention, however, can also be advantageously applied to IGBT""s.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a low impedance VDMOS semiconductor component, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.